Electron discharge device cavity resonator having a plurality of perforated members alternately positioned at right angles to the beam axis



RYOKA 'SAWADA ET AL 3,389,292

PLURALITY D E N 0 I T IS mm PA YM LA EE TB A NE RH ET T L0 AT 53 RE EL 86 MN EA M T DH EG TI AR R OT FA R E P. F 0

June 18, 1968 ELECTRON DISCHARGE DEVICE CAVITY RESONATOR HAVING A 5 6 9 l O 3 v 0 N d e l i F INVENTORS RYaKfl snwnon YOICHI Kan/5K0 Q04 91. Ch 9.

ATTORNEY United States Patent 3,389,292 ELECTRON DISCHARGE DEVICE CAVITY RES- ONATOR HAVING A PLURALITY 0F PER- FORATED MEMBERS ALTERNATELY POSI- iljggJED AT RIGHT ANGLES TO THE BEAM Ryoka Sawada, Kokubnnji-shi, and Yoichi Kaneiro, Hachioji-shi, Japan, assignors to Hitachi, Ltd., T okyo, Japan, a corporation of Japan Filed Nov. 30, 1965, Ser. No. 510,548 Claims priority, application Japan, Dec. 9. 1964, 39/613,853, 39/68,854; Dec. 18, 1964, 39/71,059, 39/71,060

4 Claims. (Cl. 315-3.6)

ABSTRACT OF THE DISCLOSURE An electron discharge device of the high power, high frequency type including a cavity resonator former as a multi-gap slow wave structure having four support plates provided at equally circumferentially spaced positions on the inner wall of the cavity resonator and disposed oppositely to one another in pairs, and a plurality of first and second perforated members alternately disposed at right angles to the axis of the discharge device, each having an electron beam passage aperture and being supported by alternate pairs of support plates.

This invention rel-ates to electron tube devices and more particularly to those adapted for use in the field of microwave applications.

Microwave power has heretofore found one of its applications in the field of microwave heating and a magnetron has been utilized for this purpose because it is an electron tube showing the highest efficiency for this type of service. The magnetron, however, has not been altogether satisfactory in that it is liable to be affected by high frequency and has a relatively short service life because its cathode portion operates in a region of an electric field at high frequency. An inconvenience involved in the magnetron is the necessity of providing a filter circuit therein in order to avoid leakage of high-frequency waves from its cathode portion. The use of la klystron which is an electron tube having a long service life and suitable for generation of high power may be considered as the possible alternative, but a drawback involved in a multi-cavity klystron having a high efficiency is that it has a complex structure and is quite expensive. A klystron of the type having a feedback circuit therein for generation of output energy by self-oscillation has previously been proposed, but this type of klystron has also been unsatisfactory due to the fact that its efiiciency is relatively low giving rise to uneconomical power loss.

It is therefore the primary object of the present inven tion to provide an electron tube device adapted for microwave generation which is small-sized and yet has a relatively high efficiency.

A further object of the present invention is to provide an electron tube device including a novel resonant slow wave structure adapted for self-exciting modulation of the electron beam.

Another object of the present invention is to provide an electron tube device equipped with a novel coupling construction for a resonant slow wave structure and an output cavity resonator.

Still another object of the present invention is to provide an electron tube device equipped with a novel water cooling system.

According to the present invention, there is provided an electron tube device comprising an electron gun for emitting a beam of electrons, a cavity resonator for im 3,389,292 Patented June 18, 1968 "ice parting modulation to the electron beam, an output cavity resonator, focusing coil mean-s for focusing the electron beam, and a collector for collecting the electron beam, said cavity resonator being of multi-gap slow wave structure having four support plates provided at equally circumferentially spaced positions on the inner wall of said cavity resonator and extending in a direction parallel to the axis of the electron beam with two support plates opposite to each other forming a pair, and a plurality of first and second perforated members alternately disposed in suitably spaced relation at right angles with respect to the axis of the electron beam, said first and second members each having an electron beam passage aperture centrally thereof and being supported by the alternate pairs of said support plates so that said slow wave structure can operate with the fundamental w-ave having a negative group velocity.

The above and other objects, advantages and features of the present invention will become apparent from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view showing the structure of one embodiment of the present invention;

FIG. 2 is a longitudinal sectional view showing the structure of another embodiment of the present invention;

FIG. 3 is a longitudinal sectional view showing the structure of part of a slow wave circuit used as a multigap resonator in the embodiment of the invention;

FIG. 4 is a sectional view taken on the line c-c' in FIG. 3;

FIG. 5 is a sectional view taken on the line d-d in FIG. 1; and

FIG. 6 is a sectional view taken on the line e-e' in FIG. 2.

Referring to FIG. 1, the electron tube device according to the invention includes a multi-gap resonant structure 3 and an output cavity 4 disposed between an electron gun 1 generating a beam of electrons and a collector 2 collecting the electron beam emitted from the electron gu-n 1. The multi-gap resonant structure 3 is shown as a short length portion of a slow wave circuit as shown in FIGS. 3 and 4, FIG. 4 being a sectional view taken on the line c-c in FIG. 3. This slow wave circuit forming the multi-gap resonant structure 3 comprises four support plates 6, 7, 8 and 9 analogous to ridge portions of a ridge waveguide. These four support plates are secured to the inner Wall of a cylindrical hollow conductor 5 at positions equally circumferentially spaced from each other and extend in parallel with the axis of the electron beam, with two support plates opposite to each other ilorming a pair. A plurality of perforated members 10, 11, 1 2, 13 and 14 of non-magnetic material each having an electron beam passage aperture centrally thereof are parallelly disposed in the cylindrical hollow conductor 5 in a manner such that they are spaced a predetermined distance from each other and are alternately secured at opposite ends to the alternate pairs of the support plates. Thus, the adjacent perforated members are disposed in cross relation with each other with their central electron beam passage apertures aligned with the electron beam axis. Now consider an electric field appearing in each operating gap along the electron beam axis relative to an electromagnetic wave traveling through the slow wave circuit. At the cut-off frequency of the fundamenal wave in the pass band of this circuit, the r-f potentials of the perforated members 10, 11 and 12 secured to the support plates 6 and 7 are the same, While the r-f potentials of the perforated members 13 and 14 secured to the support plates 8 and 9 are also the same, but the former and the latter r-f potential are different from each other in their sign. A capacitance is generally provided by the opposite perforated members forming therebetweeu the operating gap and the electric fields established in these operating gaps are alternately opposite is phase with each other. Therefore, in the slow wave circuit described above, the fundamental wave has a negative group velocity.

The hollow conductor 5 of cylindrical shape has been referred to in the above description, but the conductor may for example, have a rectangular cross-sectional shape. In order to facilitate the securing of the perforated members at the predetermined positions in the hollow conductor, cutouts may suitably be provided on the inside edge of the hollow conductor. It is generally preferable that the spacing between the inner wall of the hollow conductor and each end of the perforated member, that is, the length of each support plate, is made slightly greater than the spacing between the adjacent perforated members in order that an unnecessary capacitance is added to that portion. This perforated member commonly takes the form of a rectangular tablet, but may take any other shape as desired. In some cases, the opposite ends of these perforated members may extend to abut the inner wall of the hollow conductor.

In lieu of the perforated members of non-magnetic material used in the above-described slow wave circuit, those of a metal having high permeability such as pure iron may be used. In this latter case, when a magnetic field is applied in the axial direction of the electron beam, reluctance along the electron beam axis, especially the reluctance in the vicinity of the electron beam passage apertures shows a decrease due to the presence of such magnetic material so that the magnetic flux along the electron beam axis can be increased. With the use of the perforated members of pure iron, a periodically varying magnetic field distribution with the maximum flux density of 540 gauss and the minimum flux density of 240 gauss can be obtained on the electron beam axis, whereas the flux density on the electron beam axis is 420 gauss in case of the perforated members of, for example, copper material. Since this magnetic field distribution appears in a manner that the magnetic flux density becomes maximum at the operating gap between the perforated members, any dispersion of electrons by the r) electric field at the operating gap can effectively be prevented. With such magnetic field, ripples tend to develop at the outer peripheral portion of the electron beam, but the electron beam transmission factor would not be impaired because the electron beam expands at the operating gap and is constricted to a minimum diameter at the position of the electron beam passage aperture of the perforated member. Accordingly, the use of magnetic material leads to an advantage that the size of a magnetic field focusing coil or a permanent magnet can be made smaller. Further, copper plating or the like may be applied to the perforated members of magnetic material to reduce the loss due to a high-frequency current flowing on the surface thereof and to improve the rate of heat conduction.

The above-described slow wave circuit can also be used as a resonator as in case of a common slow wave circuit by arranging in a manner that opposite ends thereof are suitably terminated in reactances. For example, the left-hand side end of the above-described slow wave circuit may be short-circuited by the wall of the hollow conductor, and an electro-rnagnetic wave may be admitted into the circuit from the right-hand side thereof. Then, a standing wave appears in the circuit. When the potential of the shorted conductor wall is taken as a reference, the potential at the support plates 6 and 7 becomes progressively higher than the reference potential towards the right and the potential at the support plates 8 and 9 becomes progressively lower than the reference potential towards the right within a first range of /4 guide wave-length measured from the left-hand side end of the circuit. In this range, therefore, adjacent electric fields appearing between the perforated members forming the operating gaps are out of phase with each other and the field distribution is such that voltage amplitude makes an increase towards the right. In the succeeding range of substantially /4 guide Wavelength, field distribution is such that voltage amplitude decreases.

In the ultra-high frequency electron tube device having the multi-gap resonant structure 3 as described above, the ends of the four support plates 6, 7, 8 and 9 on the electron gun side are shorted by an outer casing 15 for the electron gun 1. At that end of the multi-gap resonant structure 3 adjacent to the output cavity 4, the ends of the support plates 8 and 9 are connected with an output cavity partition 16, while those ends of the support plates 6 and 7 on the side of the output cavity 4 are not connected with the output cavity partition 16 but are opencircuited in a high-frequency circuit sense.

As a matter of principle, the resonance frequency of the multi-gap structure 3 is determined by the cut-oif frequency of the slow wave circuit, the length of the circuit, terminal conditions of the circuit, etc. Experimentally, a predetermined resonance frequency can be obtained by varying the capacitance between the perforated members 10, 11, 12, 13 and 14 and the inside diameter of the hollow conductor 5.

From the foregoing description, it will be understood that the electric field distribution in the multi-gap resonant structure 3 at the fundamental resonance frequency is such that the adjacent electric fields are of opposite phase with each other and the r-f voltages at the operating gaps successively increase in the advancing direction of the electron beam from the electron gun. When the electron tube is in operation, the electron beam is successively subjected to velocity modulation by the rj voltages at the respective operating gaps and an improved efficiency can be obtained since the velocity modulation is effectively imparted to the beam having a distributed velocity. Separate disposition of the oscillator section and the output cavity provides an additional advantage that no frequency variation results from variation in a load and thus a stable operation can be attained.

In FIG. 2, there is shown another embodiment according to the invention, in which like reference numerals are used to denote like parts appearing in FIG. 1. FIG. 2 illustrates a case in which a multi-gap resonant structure 3 is coupled to an output cavity resonator 4. Or more pre cisely, those ends of support plates 6 and 7 on the side of the output cavity 4 extend through respective openings 18 and 19 provided on an upper output cavity partition 16 into the output cavity 4 to terminate at an lower output cavity partition 17. These extensions of the support plates 6 and 7 extending through the respective openings 18 and 19 are clearly shown in FIG. 6 which is a sectional view taken on the line e-e' in FIG. 2.

The coupled type of cavity resonator according to the invention comprising the combination of the multi-gap resonant structure 3 and the output cavity resonator 4 as described above operates in the following manner. The multi-gap resonant structure 3 and the output cavity resonator 4 are coupled to each other to form a combined circuit through the coupling openings 18 and 19 provided on the upper partition 16 of the output cavity resonator 4, while the extensions of the support plates 6 and 7 forming parts of the multi-gap resonant structure 3 act to further strengthen the coupling of both circuits and at the same time to regulate the resonance frequency of the output cavity resonantor 4. This resonance frequency can suitably be varied by varying the inside diameter of the extensions of the support plates 6 and 7.

High-frequency voltage appearing at an operating gap 34 in the output cavity resonator 4 is out of phase or, in some cases, in phase with voltage appearing at a gap between the partition 16 and a perforated member 11 adjacent thereto. It has been experimentally found that these opposite-phase and in-phase relations between the voltages are determined by the following conditions. Or more precisely, where no such openings 18 and 19 are provided, the multi-gap resonant structure 3 and the output cavity 4 are two resonators independent of each other. When however both are coupled together through these openings 18- and 19, the resonant frequency and electric field distribution at the gaps as a whole vary depending on the difference between the intrinsic resonant frequencies of both circuits and the coupling strength between both circuits. In the resonant circuits thus coupled together as a whole, two resonant points appear in the vicinity of the two fundamental intrinsic resonant frequencies. At the lower resonant frequency, the voltage appearing at the gap in the output cavity 4 becomes opposite in phase with respect to the voltage appearing at the adjacent gap in the mnlti-gap resonant structure 3. In order to cause the electron tube device to operate at a frequency in the vicinity of the lowest resonant frequency, the intrinsic resonant frequency of the multi-gap resonant structure 3 may be made higher than the intrinsic resonant frequency of the output cavity 4 so that the voltage appearing at the gap in the output cavity 4 can be made higher than the voltage appearing at each gap in the multi-gap resonant structure 3. Thi intrinsic resonant frequency can easily be varied by varying the inside diameter of the hollow cylinder forming the resonant cavity. For example, the resonant frequency can be made higher by reducing the inside diameter of the multi-gap resonant cavity. Conversely, at the higher resonant frequency of the resonant circuits coupled together as a whole, the voltage appearing at the gap in the output cavity 4 becomes in phase with the voltage appearing at the adjacent gap in the resonant structure 3. Therefore, the intrinsic resonant frequency of the output cavity 4 may be made higher than the intrinsic resonant frequency of the multi-gap resonant structure 3 so that the electron tube device can operate with the voltage at the output cavity gap made higher than the voltage appearing at each gap in the resonant structure 3. It will thus be apparent that the abovedescribed embodiment of the electron tube device of the present invention is advantageous in that its shape can easily be varied to deal with any operating conditions suitable for a particular service intended thereby.

As described above, the electron tube device according to the present invention is provided with five gaps for interaction with an electron beam and rf voltages appearing at these gaps are alternately out of phase with each other and successively increase along the advancing direction of the electron beam. The spacing between the adjacent gaps or the pitch thereof is made successively narrower towards the output cavity 4. With an electron tube which delivers an output of l kilowatt with a microwave frequency of 2450 megacycles per second and a cavity voltage of about 6 kilovolts, for example, the relative amplitudes of voltages in the respective gaps are 0.08, 0.15, 0.24 and O.22 in the order of the one on the electron gun side to the one on the output cavity side provided that the voltage amplitude at the output gap is taken as 1.0. The total length from the first gap to the output cavity gap is 28.4 millimeters. The electron beam emitted from the electron gun is subjected to velocity modulation by the first four gaps and is then subjected to density modulation by the bunching action imparted thereto in its way to the output cavity gap. The electric field at the output cavity gap has such a phase that the high density portion of the beam is decelerated thereby so that a highfrequency output can be derived from the output cavity gap. When the 'IT-mOdG is employed in the phase relation between electric fields in the gaps, the above condition can be satisfied selectively in a manner that the electron transit angle from gap to gap has a value of about 7r radians or a smaller value than this.

The hi gh-frequency power developed in the output cavity 4 is fed through output slots 32 and 33 provided on the partition 17 of the output cavity 4 as shown in FIG. 5 and then through a coaxial circuit section in which an outer wall 29 of the collector 2 is the central conductor.

The high-frequency power is then fed through an evacuated dome 22 of dielectric material into a waveguide 23 for supply to an external load. In addition to the coupling construction of the invention including the multi-gap cavity resonator as described above, a coupling construction similar to the above may easily be obtained with a moditied form of such rnulti-gap cavity resonator or a cavity resonator with a helix of wire.

The electron tube device of the invention can effectively be cooled by a cooling system as shown in FIG. 1. Cooling water admitted through an inlet a passes through water passages 25 and 26 provided in focusing coil means 24. Each of the water passages 25 and 26 extends over a width of a quarter of the inner periphery of the focusing coil means 24 so as to absorb the heat generated in the cavities 3 and 4 and the heat generated from the focusing coil means 24. The cooling water passed through the water passage 25 flows through a communication passage 27 provided below the output cavity partition 17 into a plurality of conducting ports 21 extending through the right-side half of the outer wall 20 of the collector 2 to join at an end passage 28. From this end passage 28, the cooling water flows through a plurality of conducting ports 21 extending through the other half of the outer wall 20 of the collector 2 and through a communication passage 29 and the water passage 26 to an outlet b. 0- rings 30 and 31 are provided to prevent the cooling water from leaking outwardly. A portion of the cooling water may be branched from the water passage 25 to the water passage 26 to directly cool the electron tube body.

What we claim is:

1. An electron tube device comprising an electron gun for emitting a beam of electrons, a cavity resonator for imparting modulation to the electron beam, an output cavity resonator, means for focusing the electron beam, and a collector for collecting the electron beam, said cavity resonator being of multi-gap slow wave structure having four support plates provided at equally circumferentially spaced positions on the inner wall of said cavity resonator and extending in a direction parallel to the axis of the electron beam with two support plates opposite to each other forming a pair, and a plurality of first and second perforated members alternately disposed in suitably spaced relation at right angles with respect to the axis of the electron beam, said first and second members each having an electron beam passage aperture centrally thereof and being supported by the alternate pairs of said support plates so that said slow wave structure can operate with the fundamental wave having a negative .group velocity.

2. An electron tube device according to claim 1, in which said support plates for said perforated members of said multi-gap slow wave structure are short-circuited at those ends adjacent to said electron gun and opencircuited at those ends adjacent to said output cavity resonator so that said multi-gap slow wave structure can operate in a manner that amplitude of voltages appearing at a plurality of operating gaps defined by said perforated members successively increase in the advancing direction of the electron beam whereby a high-frequency output can be derived from said output cavity resonator disconnected from said multi-gap slow wave structure in a high-frequency circuit sense.

3. An electron tube device according to claim 1, in which said support plates for said perforated members of said slow wave structure are short-circuited at those ends adjacent to said electron gun and coupling means is provided to couple said slow wave structure to said output cavity resonator to thereby form a compositely coupled resonator, said coupled resonator being operative in a manner that electric fields in adjacent operating gaps defined by said perforated members are out of phase with each other and voltage appearing at an operating gap in said output cavity resonator is greater than the voltages appearing at the operating gaps between said perforated members in said slow wave structure.

4. An electron tube device according to claim 1, in which an outer wall of said collector is so arranged a to serve as the central conductor of a coaxial line in a high frequency output circuit and a cooling water system is provided in order to cool said focusing coil means and said collector, said cooling water system including cooling water passages extending substantially along the interface between said focusing coil means and the electron tube body and a plurality of cooling water conducting ports connected with said cooling water passages and extend- No references cited.

ELI LIEBERMAN, Primary Examiner.

HERMAN K. SAALBACH, Examiner.

S. CHATMON, In, Assistant Examiner. 

